Synthesis of composition-controlled iron-based nanoparticles for application to magnetic refrigeration

在多元醇溶液中合成了由fcc-FePt合金相和弱晶化的Fe-和Pt-氧化物相组成的FePt纳米粒子。在573 K以上的温度下，在5%H_2/Ar混合气体中热处理的样品的X射线衍射图中，观察到对应于L1_0型超晶格线的衍射峰。这是非常有可能的，这种无序有序的FePt纳米粒子的转换是伴随着组成的均匀化，由于减少结晶不良的Fe-和Pt-氧化物相。在含铁、镍盐的多元醇溶液中析出的中间细颗粒，在5%H_2/Ar混合气体中退火后被还原。这种技术可用于在宽的组成范围内合成FeNi合金细颗粒。

FePt nanoparticles composed of crystalline fcc-FePt alloy phase and poorly crystallized Fe- and Pt-oxide phase were synthesized in polyol solution. In X-ray diffraction patterns of the specimens which were heat-treated at temperatures above 573 K in a mixture of 5%H_2 in Ar, diffraction peaks corresponding to superlattice lines of L1_0 type structure were observed. It is highly probable that such disorder-order transformation of FePt nanoparticles is accompanied by compositional homogenization due to the reduction of the poorly crystallized Fe- and Pt-oxide phase. It was also shown that intermediate fine particles precipitated in poyol solution containing Fe and Ni salts were reduced during post-annealing in a mixture of 5%H_2 in Ar. Such technique is useful to synthesis FeNi alloy fine particles over a wide composition range.